The present invention relates, in general, to a structural or chassis component for a motor vehicle, and a method of making such a structural or chassis component.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Cut edges of compressed parts of sheet metal, in particular a structural or chassis component made of high strength steel or light metal for use in motor vehicles, oftentimes constitute weak points when subjected to high stress, in particular when exposed to a dynamic load or in the event of a crash. Under those circumstances, cracks develop in the area of the cut edges as a result of high stress to which these edge zones are exposed during operation. When the edge zones are mechanically cut, the texture changes and microcracks develop which render the structural or chassis components more susceptible to develop cracks. At the same time, the thickness of the structural or chassis components along the cut edge is reduced as a result of the necessary cutting pressure. Using thermal cutting processes cannot overcome these problems because the edge area is generally weakened by process-related notches along the cut edge. When high strength steel is involved, its ultimate strength is weakened by the heat impact. As a consequence, finished structural or chassis components not only are prone to fail but encounter already during the manufacturing process cracks or contractions in the outer regions as a result of loads caused by flaring, trimming, beveling, or the like processes for example.
An attempt to eliminate tensile stress and microcracks along the length edges of torsion members of twist-beam axles is described in German Pat. No. DE 196 42 995 C1. The length edges are hereby upset to generate residual compressive stress. As a result, the surfaces of the cut edges are smoothed and microcracks are cold-welded.
German Offenlegungsschrift DE 33 43 709 A1 discloses a method of making a frame part for motor vehicles. The frame part is hereby formed from a blank in a press tool, with the blank being partially rolled to provide length sections of different thickness. The method involves formation of longitudinal grooves in the blank at a slight distance to the length edges and subsequently upsetting of the length edges.
For a number of reasons, the various proposals are endowed with drawbacks and shortcomings relating for example to manufacturing techniques or to the effect that is hoped to be obtained but may not always be realized.
It would therefore be desirable and advantageous to provide an improved method of making a structural or chassis component to obviate prior art shortcomings and to provide enhanced edge properties so as to produce a structural or chassis component that is reliable in operation even when exposed to high stress.